This invention relates to a method for forming threads on a workpiece and more particularly, to a method of producing non-symmetrical thread forms by modification of the process known as thread whirling.
Prior to the present invention, many well-known techniques have been employed to form threads. These techniques employed various machines which ranged from a relatively simple engine lathe to sophisticated milling and thread hobbing machines. Generally, such techniques have the disadvantage that several passes of the cutting tool over the workpiece are required to form the final thread configuration.
This repetition of operations can result in a time consuming and expensive method of cutting threads. If a single longitudinal pass of the cutting tool over the workpiece is used, forming time can be greatly reduced. Another disadvantage of prior techniques is that threads cannot be cut in very hard material. It is necessary to cut the thread and then harden the material.
In order to form a thread on hardened metals with a single longitudinal pass of the tool over the workpiece a technique sometimes referred to as "thread whirling" has been developed. In this method of cutting threads on a workpiece, the cutting tool is in continuous circular cutting contact with the workpiece to thereby permit the cutting of harder metals than is possible with other thread cutting techniques. In "thread whirling" the cutting tool is rotated at a high speed on an axis which is parallel and eccentric to the axis of the workpiece. Relative rotation is established between the workpiece and the cutting tool so that the circular path of the cutting tool orbits about the workpiece at a slower speed. The cutting tool is advanced along the length of the workpiece in spaced relation to the relative movement between the workpiece and the cutting tool so that a thread is formed. The pitch of the groove cut by each revolution of the cutting tool is a small fraction of the pitch of the formed thread. The resultant thread has a smooth surface not readily obtainable with other methods of cutting threads.